This application relates to processes for decolorization of sugar syrups, and more particularly to decolorization of sugar syrups using functionalized adsorbents containing weak-acid cation exchange groups or weak-base anion exchange groups.
Decolorization of aqueous sugar syrups derived from corn, beets and sugar cane has traditionally relied upon carbonaceous adsorbents such as bone char or powdered and granular activated carbons. Although these carbonaceous materials themselves are inexpensive, the processes employing them tend to require expensive equipment and intensive labor. In a typical industrial decolorization process, powdered carbon is used in a batch adsorption process. After decolorization the sugar syrup must be filtered, as a separate step, to remove the carbon for reclamation and regeneration. In a continuous process the sugar syrup passes through beds of granular activated carbon for decolorization; periodically a fraction of the carbon bed is removed for regeneration and that carbon is replaced by either regenerated or new carbon. Carbon regeneration is a high-temperature process requiring fuel for the regeneration furnace and carbon losses during the regeneration can approach ten weight percent. Also, thermal regeneration destroys the color bodies removed during decolorization, preventing their recovery for study or other uses.
Ion exchange resins have been proposed for sugar syrup decolorization; they permit continuous use of the treatment column and in situ regeneration using readily available chemicals such as caustic and acid, and their long operational life and less expensive equipment and handling, compared to carbon, in most cases offsets their higher initial expense. Unfortunately, ion exchange resins have a low capacity for adsorbing color bodies from solution compared to carbon and require much larger quantities of regenerants to remove the color bodies than to remove typical ionic species. Additionally, ion exchange resins do not effectively remove impurities such as HMF (5-hydroxymethyl-2-furfural) that increase the color of sugar syrups on standing and during further processing.
U.S. Pat. Nos. 4,950,332 and 5,416,124 propose using synthetic polymeric functionalized adsorbents prepared by swelling a porous styrene/divinylbenzene copolymer in a swelling solvent, adding chloromethyl groups to the polymer via a chloromethylation reaction and post-crosslinking the swollen structure with methylene groups in the presence of a Friedel Crafts catalyst, to form a macronet structure that remains when the solvent is removed. The macronet structure, however, contains a large amount of microporosity comparable to that of activated carbon, and as the above U.S. Pat. No. 5,416,124 indicates, such microporosity is expected to increase adsorption capacity but degrade adsorption and regeneration kinetics.
The present invention seeks to overcome the problems associated with prior art processes for decolorizing sugar syrups by using a functionalized adsorbent having a combination of properties not found in adsorbents heretofore available, that is, a high level of mesoporosity and macroporosity for good adsorption kinetics, stability and easy regeneration and a high adsorption capacity without the presence of microporosity.